Method and device for drying a compressed working fluid

ABSTRACT

We disclose methods and means for drying a compressed working fluid in which a branch current of hot unsaturated working fluid is conducted directly from the compressor to the regeneration zone of a sorbtion-drying apparatus comprising a rotatable drying element driven by a motor. We also disclose means controlled by the unloading device of the compressor for disconnecting the driving of the drying element when the compressor unloads.

United States Patent [191 Sylvan et al.

[451 Apr. 30, 1974 METHOD AND DEVICE FOR DRYING A COMPRESSED WORKINGFLUID [75] Inventors: B0 Anders Sylvan; Nils Axel Agren,

both of Nacka, Sweden [73] Assignee: Atlas Copco Aktiebolag, Nacka,

Sweden 22 Filed: July 14,1972

21 Appl.No.: 271,982

[30] Foreign Application Priority Data Augf6, 1971 Sweden lOO87/7l [52]US. Cl 34/9, 34/15, 34/95 [51] Int. Cl. F26b 3/00 [58] Field of Search34/9, 15, 95

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 335,323 5/1971Sweden Primary Examiner-John J. Camby Attorney, Agent, or FirmEric Y.Munson [57] ABSTRACT We disclose methods and means for drying acompressed working fluid in which a branch current of hot unsaturatedworking fluid is conducted directly from the compressor to theregeneration zone of a sorbtiondrying apparatus comprising a rotatabledrying element driven by a motor. We also disclose means controlled bythe unloading device of the compressor for disconnecting the driving ofthe drying element when the compressor unloads.

13 Claims, 2 Drawing Figures PATENTEDAPR 30 NW SHHT 2 OF 2 WE Q 5.0g

METHOD AND DEVICE FOR DRYING A COMPRESSED WORKING FLUID BACKGROUND OFTHE INVENTION The present invention concerns a method and a device fordrying a compressed working fluid such as air or some other gascompressed in a compressor. It is known to use so-called sorption-dryingapparatus for drying air or other gases, whereby such apparatuses arereferred to that comprise a vessel including a wateradsorbent, such assilica gel, lithium chloride or other like substances or water-absorbingmaterial, such as asbestos sheathing, porous bodies or the like or acombination of both. It is also known to include a rotatable dryingelement in such drying apparatus in which the working fluid passesthrough a drying zone and in which a regeneration zone is arranged,which is passed by a working fluid for regeneration of the dryingelement. A known drying element of this type consists of pleatedasbestos sheathing, which has been impregnated with lithium chloride andpossibly been armoured to resist the mechanical strains and which formsa rotor with a great number of axial channels, which rotor is arrangedin a housing which includes separate conduits for the working fluidwhich is to be dried and for the fluid used for the regeneration. Dryingplants of the above mentioned type for drying air of atmosphericpressure do not offer any great problem. But as soon as drying ofcompressed air or some other compressed gas is concerned, a great dealof problems arise which are closely allied to the special properties andoperating conditions of compressed air or compressed gas in a compressorplant. A drawback with known drying plants for compressed air orcompressed gas is that they include relatively expensive heatexchangers. Another drawback is that they are sensitive to differentloadings of the compressor. In known sorption-drying apparatusescomprising a rotatable drying element, the drying element iscontinuously driven by a motor. When the compressor runs unloaded, thereis no fluid supplied to the regeneration zone of the drying apparatusfor regeneration of the drying element. As a a consequence a wet part ofthe drying element may pass the regeneration zone when the compressorruns unloaded and thus enter the drying zone in a wet condition. Thiswill of course spoil the drying result. The invention is aiming to bringabout a method and devices for drying a compressed working fluid byusing a minimum of heat exchangers and by which the operating conditionsof the compressor will not prejudice the drying result or the dryingapparatus. The invention is mainly characterized by those methods anddevices that are stated in the below given claims.

BRIEF DESCRIPTION OF THE DRAWINGS The method according to the inventionis more closely described below in conjunction with two schematicdiagrams.

FIG. 1 shows one embodiment of the invention. FIG. 2 shows anotherembodiment of the invention.

SUMMARY OF THE INVENTION The diagrams show examples of devices forcarrying out the method in two different modifications. In a broad sensethe method according to the invention is based upon the novel conceptthat a compressed working fluid compressed in a compressor is dried byconducting a main current of the working fluid from the compressorthrough an after-cooler including a water separator and after thatthrough a drying zone in a regenerative sorption-drying apparatus, andby conducting a branch current of hot unsaturated working fluid from thecompressor through a regeneration zone in the drying apparatus andthereafter via an after-cooler including a water separator together withthe main current through the drying zone to a delivery conduit. Themethod according to the invention is based on the observation that thehot working fluid, which is delivered by the compressor, has such a hightemperature and such a low relative moisture proportion that a branchcurrent can be separated and used for regeneration by conducting itthrough a regeneration zone in the drying apparatus for carrying awaythe moisture which has been transferred to the regeneration zone fromother parts of the drying apparatus, where it has earlier been taken up,through the rotation of the drying element. The main current of theworking fluid is conducted from the compressor through an after-coolerincluding a water separator and after that to the drying zone of thesorbtion-drying apparatus. The branch current used for regeneration issuitably conducted via a cooler ineluding a water separator from theregeneration zone to the main current and together with this through thedrying zone. The method is suitably carried out so that the pressure inthe regeneration zone always is kept somewhat lower than the pressure inthe drying zone in order to permit a possible leakage of working fluidto pass from the dry part to the regeneration zone.

DESCRIPTION OF A SPECIFIC EMBODIMENT In the diagram shown in FIG. 1 acompressor of arbitrary kind, for instance a two-stage piston compressoror a screw compressor is indicated by 1, 33, which is driven by a motor34 and supplied with working fluid, for instance air, via an intakefilter 2 and a conduit 3. The compressor may include an intermediatecooler as indicated at 35. From the compressor the hot compressed airflows through a conduit 4, 5 to an aftercooler 6 including a waterseparator from which the air flows as a main air current through aconduit 7 and an ejector 8 to a sorption-drying apparatus 9. Thesorption-drying apparatus 9 includes a rotor 10, which forms a dryingelement that in a known manner may consist of pleated asbestos sheatingwhich has been impregnated with lithium chloride and reinforced in asuitable manner with a metal wire armanent or the like to resist themechanical strains during different moisture conditions. The rotor 10 ismade in such a way that the working fluid is able to flow axiallythrough the rotor through a great number of relatively thin channels. Asector of the rotor is at its ends axially shielded with shields ll, 12so that a regeneration zone 13 is formed in the rotor, which during therotation of the rotor goes round the rotor in succession. The rest ofthe rotor forms a drying zone 14. Instead of letting the rest of therotor form a drying zone, a cooling zone may be formed between theregeneration zone 13 and the drying zone 14. This has for its purpose tocool the rotor material before it enters the drying zone. The coolingmay for instance be accomplished with dry gas or wet gas, which afterhaving passed the cooling zone is conducted back to the main current inthe same manner as the regeneration gas or together with it. There is nocooling zone shown in the drawings. The rotor is driven by a motor 15which, when the compressor is electrically driven, is suitablyconstituted by an electro-motor including a suitable gearing forreducing the number of revolutions to that at which the rotor rotates.The motor is supplied with current from an electric line 16 via a switch17, which is suitably manoeuvred with compressed air in connection withthe unloading device 18 of the compressor via a manoeuvring-cylinder 19which closes the switch 17 when the compressor is loaded.

The compressed air or compressed gas dried in the drying zone 14 isconducted to suitable consumers through a pressure conduit 20 for dryair or gas. For the regeneration of the sorption-drying apparatus, abranch conduit 21 is branched from the conduit 4, 5. The conduit 21includes a restriction 22 constituted by a throttle-disc or anadjustable throttle-valve. A branch current of the working fluid isconducted directly from the pressure side of compressor through theconduit 21 to the regeneration zone 13 in the drying apparatus. Thisbranch current has in a compressor plant for a pressure of for instance7 atmospheres above the atmospheric pressure, a temperature of more than100 centigrades and at this temperature a low relative moistureproportion (for instance 20-30 percent) and can, therefore, partly heatthe rotor material in the regeneration zone and partly carry away themoisture therefrom. From the regeneration zone the branch current flowsthrough the conduit 23 to a cooler 24 including a water separator andtherefrom through a conduit 25 to the suctionside of the ejector 8. Thebranch current is drawn into the main current by the ejector 8 and moveson together with the latter current into the drying zone 14 of thedrying apparatus. The after-cooler 6 includes a cooling element 26,which is fed with cooling-water through a conduit 27 and the cooler 24includes a cooling element 28, which is fed with cooling-water from aconduit 29. 30 and 31 are condensed-water separators of conventionalkind included in the coolers.

The restriction 22 and the ejector 8 are so chosen and dimensioned thata somewhat lower pressure is obtained in the regeneration zone 13 thanin the drying zone 14. By reason thereof any possible leakage from onezone to another will be constituted by dried air or dried working fluidflowing into the regeneration zone.

Upon occurrence of a possible decrease in the load ing of thecompressor, the plant according to FIG. 1 will still work substantiallyas when fully loaded. When the compressor is unloaded the main currentthrough the cooler 6 and the conduit 7 is, however, interrupted andconsequently no branch current can pass through the regeneration zone.The device is, therefore, so made that the unloading device of thecompressor upon unloading of the compressor, simultaneously disconnectsthe motor 15 which normally drives the drying element 10. Thereby a morereliable function of the drying apparatus is obtained, and the dryingresult will not be afiected.

In the modification according to FIG. 2 the cooler 24 for the branch aircurrent or branch gas current is eliminated and an ejector 32 has beenarranged in the conduit leading to the after-cooler 6 instead of theejector 8 in conduit 7. The rest of the plant according to FIG. 2 ismade in the same manner as the plant according to FIG. 1 and equivalentdetails have, therefore, been indicated with the same reference numeralsas in FIG. 1 and will not be described again. The working fluid currentused for regeneration is in the modification according to FIG. 2supplied through the conduit 23, 25 to the suction side of the ejector32 and passes together with the main air current through the aftercooler6. The pressures indicated in FIG. 1 are related in the following way: Pis higher than P,, which is higher than P and higher than P which is thepressure in the regeneration zone. Like conditions must of courseprevail in the plant according to FIG. 2 in which, however, the ejector32 has to overcome a larger pressure decrease than the ejector 8 in theplant according to FIG. 1. The cooler 6 in FIG. 2 will also becomebigger than in FIG. 1.

The above described methods and devices are only to be regarded asexamples which may be modified in different ways within the scope of theclaims. The ejectors may for instance be substituted by ordinary pumps.In electrically driven compressor plants electrical supervision devicesfor unloading may be used to supervise the motor electrically anddisconnect it when unloading. A pneumatically or hydraulicallysupervised pressure fluid motor may be arranged instead of 15. Thecoolers 6, 24 may be air-cooled and the water separators 30, 31 may beintroduced separate from the coolers. The drying apparatus may consistof a number of drying towers or the like.

What we claim is:

1. The method of drying hot working fluid from a compressor comprising:

a. passing a main current of hot compressed working fluid in a mainpassage through an after-cooler to remove heat therefrom;

b. passing said cooled current through a drying zone in a regenerativesorption-drying apparatus;

c. passing a branch current of hot unsaturated working fluid from saidcompressor through a regeneration zone of said sorption-dryingapparatus;

(1. merging said currents after having been passed through saidregenerative sorption-drying apparatus, and

e. passing said dried and merged currents to a common discharge outlet.

2. A method according to claim 1, at which the branch current isrestricted so that the pressure in the regeneration zone is lower thanin the drying zone.

3. A method according to claim 1, at which the branch current is cooledtogether with the main current in the after-cooler which includes awater separator.

4. A method according to claim 1, at which a rotatable drying element ofthe sorbtion-drying apparatus is alternatingly passed through the dryingzone and the regeneration zone in succession.

5. A device for drying a compressed working fluid comprising acompressor, an after-cooler including a water separator, asorbtion-drying apparatus comprising a drying zone and a regenerationzone, a conduit for conducting hot working fluid from the compressor tothe after-cooler, a conduit for conducting the cooled working fluid fromthe after-cooler to the drying zone, a branch conduit for conducting hotworking fluid from the compressor to the regeneration zone for supplyinghot unsaturated working fluid to the regeneration zone and a conduit forconducting working fluid from the regeneration zone via a cooler to thedrying zone.

6. A device according to claim 5 comprising a restriction in the branchconduit between the compressor and the regeneration zone.

7. A device according to claim 5 in which an ejector is arranged in theconduit from the after-cooler to the drying zone and the conduit fromthe regeneration zone to the drying zone is connected to the suctionside of the ejector.

8. A device according to claim 5 in which an ejector is arranged in theconduit from the compressor to the after-cooler and the conduit from theregeneration zone to the drying zone is connected to the suction side ofthe ejector.

9. A device according to claim 7 in which the restriction, the ejectorand the flow resistances in the aftercooler, the regeneration zone andthe conduits are so dimensioned that the pressure in the regenerationzone is somewhat lower than the pressure in the drying zone when thecompressor is working loaded.

10. A device according to claim 8 in which the restriction, the ejectorand the flow resistances in the after-cooler, the regeneration zone andthe conduits are so dimensioned that the pressure in the regenerationzone is somewhat lower than the pressure in the drying zone when thecompressor is working loaded.

11. A device according to claim 5 in which the sorption-drying apparatuscomprises a motor driven rotatable element, an unloading device in thecompressor and means controlled by the unloading device for disengagingsaid rotatable element upon unloading of the compressor.

12. A device for drying a compressed working fluid comprising acompressor, a regenerative sorbtiondrying apparatus comprising arotatable drying element which is driven by a motor, an unloading deviceon the compressor and means controlled by the unloading device fordisconnecting the driving of the drying element when the compressorunloads.

13. The method of drying hot working fluid from a compressor comprising:

a. passing a main current of hot compressed working fluid in a mainpassage through an after-cooler to remove heat therefrom;

b. passing a branch current of hot unsaturated working fluid from saidcompressor through a regeneration zone in regenerative sorption-dryingapparatus;

c. merging said branch current after having passed through saidregeneration zone with said main current;

d. passing said merged currents through a drying zone in saidregenerative sorption-drying apparatus, and

e. passing the thus dried and merged currents to a discharge outlet.

1. The method of drying hot working fluid from a compressor comprising:a. passing a main current of hot compressed working fluid in a mainpassage through an after-cooler to remove heat therefrom; b. passingsaid cooled current through a drying zone in a regenerativesorption-drying apparatus; c. passing a branch current of hotunsaturated working fluid from said compressor through a regenerationzone of said sorption-drying apparatus; d. merging said currents afterhaving been passed through said regenerative sorption-drying apparatus,and e. passing said dried and merged currents to a common dischargeoutlet.
 2. A method according to claim 1, at which the branch current isrestricted so that the pressure in the regeneration zone is lower thanin the drying zone.
 3. A method according to claim 1, at which thebranch current is cooled together with the main current in theafter-cooler which includes a water separator.
 4. A method according toclaim 1, at which a rotatable drying element of the sorbtion-dryingapparatus is alternatingly passed through the drying zone and theregeneration zone in succession.
 5. A device for drying a compressedworking fluid comprising a compressor, an after-cooler including a waterseparator, a sorbtion-drying apparatus comprising a drying zone and aregeneration zone, a conduit for conducting hot working fluid from thecompressor to the after-cooler, a conduit for conducting the cooledworking fluid from the after-cooler to the drying zone, a branch conduitfor conducting hot working fluid from the compressor to the regenerationzone for supplying hot unsaturated working fluid to the regenerationzone and a conduit for conducting working fluid from the regenerationzone via a cooler to the drying zone.
 6. A device according to claim 5comprising a restriction in the branch conduit between the compressorand the regeneration zone.
 7. A device according to claim 5 in which anejector is arranged in the conduit from the after-cooler to the dryingzone and the conduit from the regeneration zone to the drying zone isconnected to the suction side of the ejector.
 8. A device according toclaim 5 in which an ejector is arranged in the conduit from thecompressor to the after-cooler and the conduit from the regenerationzone to the drying zone is connected to the suction side of the ejector.9. A device according to claim 7 in which the restriction, the ejectorand the flow resistances in the after-cooler, the regeneration zone andthe conduits are so dimensioned that the pressure in the regenerationzone is somewhat lower than the pressure in the drying zone when thecompressor is working loaded.
 10. A device according to claim 8 in whichthe restriction, the ejector and the flow resistances in theafter-cooler, the regeneration zone and the conduits are so dimensionedthat the pressure in the regeneration zone is somewhat lower than thepressure in the drying zone when the compressor is working loaded.
 11. Adevice according to claim 5 in which the sorption-drying apparatuscomprises a motor driven rotatable element, an unloading device in thecompressor and means controlled by the unloading device for disengagingsaid rotatable element upon unloading of the compressor.
 12. A devicefor drying a compressed working fluid comprising a compressor, aregenerative sorbtion-drying apparatus comprising a rotatable dryingelement which is driven by a motor, an unloading device on thecompressor and means controlled by the unloading device fordisconnecting the driving of the drying element when the compressorunloads.
 13. The method of drying hot working fluid from a compressorcomprising: a. passing a main current of hot compressed working fluid ina main passage through an after-cooler to remove heat therefrom; b.passing a branch current of hot unsaturated working fluid from saidcompressor through a regeneration zone in regenerative sorption-dryingapparatus; c. merging said branch current after having passed throughsaid regeneration zone with said main current; d. passing said mergedcurrents through a drying zone in said regenerative sorption-dryingapparatus, and e. passing the thus dried and merged currents to adischarge outlet.